1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * ee1004 - driver for DDR4 SPD EEPROMs
  4 *
  5 * Copyright (C) 2017-2019 Jean Delvare
  6 *
  7 * Based on the at24 driver:
  8 * Copyright (C) 2005-2007 David Brownell
  9 * Copyright (C) 2008 Wolfram Sang, Pengutronix
 10 */
 11
 12#include <linux/i2c.h>
 13#include <linux/init.h>
 14#include <linux/kernel.h>
 15#include <linux/mod_devicetable.h>
 16#include <linux/module.h>
 17#include <linux/mutex.h>
 18
 19/*
 20 * DDR4 memory modules use special EEPROMs following the Jedec EE1004
 21 * specification. These are 512-byte EEPROMs using a single I2C address
 22 * in the 0x50-0x57 range for data. One of two 256-byte page is selected
 23 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
 24 *
 25 * Therefore we need to request these 2 additional addresses, and serialize
 26 * access to all such EEPROMs with a single mutex.
 27 *
 28 * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
 29 * We use SMBus access even if I2C is available, these EEPROMs are small
 30 * enough, and reading from them infrequent enough, that we favor simplicity
 31 * over performance.
 32 */
 33
 34#define EE1004_ADDR_SET_PAGE		0x36
 35#define EE1004_NUM_PAGES		2
 36#define EE1004_PAGE_SIZE		256
 37#define EE1004_PAGE_SHIFT		8
 38#define EE1004_EEPROM_SIZE		(EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
 39
 40/*
 41 * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
 42 * from page selection to end of read.
 43 */
 44static DEFINE_MUTEX(ee1004_bus_lock);
 45static struct i2c_client *ee1004_set_page[EE1004_NUM_PAGES];
 46static unsigned int ee1004_dev_count;
 47static int ee1004_current_page;
 48
 49static const struct i2c_device_id ee1004_ids[] = {
 50	{ "ee1004", 0 },
 51	{ }
 52};
 53MODULE_DEVICE_TABLE(i2c, ee1004_ids);
 54
 55/*-------------------------------------------------------------------------*/
 56
 57static int ee1004_get_current_page(void)
 58{
 59	int err;
 60
 61	err = i2c_smbus_read_byte(ee1004_set_page[0]);
 62	if (err == -ENXIO) {
 63		/* Nack means page 1 is selected */
 64		return 1;
 65	}
 66	if (err < 0) {
 67		/* Anything else is a real error, bail out */
 68		return err;
 69	}
 70
 71	/* Ack means page 0 is selected, returned value meaningless */
 72	return 0;
 73}
 74
 75static int ee1004_set_current_page(struct device *dev, int page)
 76{
 77	int ret;
 78
 79	if (page == ee1004_current_page)
 80		return 0;
 81
 82	/* Data is ignored */
 83	ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00);
 84	/*
 85	 * Don't give up just yet. Some memory modules will select the page
 86	 * but not ack the command. Check which page is selected now.
 87	 */
 88	if (ret == -ENXIO && ee1004_get_current_page() == page)
 89		ret = 0;
 90	if (ret < 0) {
 91		dev_err(dev, "Failed to select page %d (%d)\n", page, ret);
 92		return ret;
 93	}
 94
 95	dev_dbg(dev, "Selected page %d\n", page);
 96	ee1004_current_page = page;
 97
 98	return 0;
 99}
100
101static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
102				  unsigned int offset, size_t count)
103{
104	int status, page;
105
106	page = offset >> EE1004_PAGE_SHIFT;
107	offset &= (1 << EE1004_PAGE_SHIFT) - 1;
108
109	status = ee1004_set_current_page(&client->dev, page);
110	if (status)
111		return status;
112
113	/* Can't cross page boundaries */
114	if (offset + count > EE1004_PAGE_SIZE)
115		count = EE1004_PAGE_SIZE - offset;
116
117	if (count > I2C_SMBUS_BLOCK_MAX)
118		count = I2C_SMBUS_BLOCK_MAX;
119
120	return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
121}
122
123static ssize_t eeprom_read(struct file *filp, struct kobject *kobj,
124			   struct bin_attribute *bin_attr,
125			   char *buf, loff_t off, size_t count)
126{
127	struct i2c_client *client = kobj_to_i2c_client(kobj);
128	size_t requested = count;
129	int ret = 0;
130
131	/*
132	 * Read data from chip, protecting against concurrent access to
133	 * other EE1004 SPD EEPROMs on the same adapter.
134	 */
135	mutex_lock(&ee1004_bus_lock);
136
137	while (count) {
138		ret = ee1004_eeprom_read(client, buf, off, count);
139		if (ret < 0)
140			goto out;
141
142		buf += ret;
143		off += ret;
144		count -= ret;
145	}
146out:
147	mutex_unlock(&ee1004_bus_lock);
148
149	return ret < 0 ? ret : requested;
150}
151
152static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE);
153
154static struct bin_attribute *ee1004_attrs[] = {
155	&bin_attr_eeprom,
156	NULL
157};
158
159BIN_ATTRIBUTE_GROUPS(ee1004);
160
161static void ee1004_cleanup(int idx)
162{
163	if (--ee1004_dev_count == 0)
164		while (--idx >= 0) {
165			i2c_unregister_device(ee1004_set_page[idx]);
166			ee1004_set_page[idx] = NULL;
167		}
168}
169
170static int ee1004_probe(struct i2c_client *client)
171{
172	int err, cnr = 0;
173
174	/* Make sure we can operate on this adapter */
175	if (!i2c_check_functionality(client->adapter,
176				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
177	    !i2c_check_functionality(client->adapter,
178				     I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
179		return -EPFNOSUPPORT;
180
181	/* Use 2 dummy devices for page select command */
182	mutex_lock(&ee1004_bus_lock);
183	if (++ee1004_dev_count == 1) {
184		for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
185			struct i2c_client *cl;
186
187			cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
188			if (IS_ERR(cl)) {
189				err = PTR_ERR(cl);
190				goto err_clients;
191			}
192			ee1004_set_page[cnr] = cl;
193		}
194
195		/* Remember current page to avoid unneeded page select */
196		err = ee1004_get_current_page();
197		if (err < 0)
198			goto err_clients;
199		dev_dbg(&client->dev, "Currently selected page: %d\n", err);
200		ee1004_current_page = err;
201	} else if (client->adapter != ee1004_set_page[0]->adapter) {
202		dev_err(&client->dev,
203			"Driver only supports devices on a single I2C bus\n");
204		err = -EOPNOTSUPP;
205		goto err_clients;
206	}
207	mutex_unlock(&ee1004_bus_lock);
208
209	dev_info(&client->dev,
210		 "%u byte EE1004-compliant SPD EEPROM, read-only\n",
211		 EE1004_EEPROM_SIZE);
212
213	return 0;
214
215 err_clients:
216	ee1004_cleanup(cnr);
217	mutex_unlock(&ee1004_bus_lock);
218
219	return err;
220}
221
222static void ee1004_remove(struct i2c_client *client)
223{
224	/* Remove page select clients if this is the last device */
225	mutex_lock(&ee1004_bus_lock);
226	ee1004_cleanup(EE1004_NUM_PAGES);
227	mutex_unlock(&ee1004_bus_lock);
228}
229
230/*-------------------------------------------------------------------------*/
231
232static struct i2c_driver ee1004_driver = {
233	.driver = {
234		.name = "ee1004",
235		.dev_groups = ee1004_groups,
236	},
237	.probe_new = ee1004_probe,
238	.remove = ee1004_remove,
239	.id_table = ee1004_ids,
240};
241module_i2c_driver(ee1004_driver);
242
243MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
244MODULE_AUTHOR("Jean Delvare");
245MODULE_LICENSE("GPL");